OK. Anyone care to look at and comment on this mock up? The crossmembers are 3" I-beam, 14 gauge. The top bar is 1 1/2" 11g. I'll be using 1 1/2" 11g flat iron for strapping. The bar atop the tank will obviously be cut so that there's two top bars. Going to bolt the I-beans to the top and bottom of the frame rails, the top bar to the I-beams, and the strapping to either the I-beam or the top bar.

http://i.imgur.com/8Q4YTnZ.jpg
http://i.imgur.com/nTjNfSq.jpg

Is this a sufficient support for a 20gal tank?

Second question: Is the I-beam better than the spare tire crossmember?

Lastly here's the shock support bar:

http://i.imgur.com/8idKTxx.jpg

1 1/2" 11g. The holes are to bolt it to the frame. I'll drill larger holes for the shock studs and weld them in. Could this be used as a crossmember for the gas tank in place of the I-beam or is it insufficient?